Cathode, lithium air battery including cathode, and method of preparing lithium air battery

ABSTRACT

The present invention relates to a cathode, a lithium air battery including a cathode, and a method of preparing the lithium air battery. A cathode configured to use oxygen as a cathode active material, the cathode including: a lithium alloy represented by Formula 1LixMy  Formula 1wherein, in Formula 1, M is Pb, Sn, Mo, Hf, U, Nb, Th, Ta, Bi, Mg, Al, Si, Zn, Ag, Cd, In, Sb, Pt, or Au, 0&lt;x≤10, 0&lt;y≤10, and 0&lt;x/y&lt;10.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2019-0002985, filed on Jan. 9, 2019, in the KoreanIntellectual Property Office, and all the benefits accruing therefromunder 35 U.S.C. § 119, the content of which is incorporated herein byreference in its entirety.

BACKGROUND 1. Field

The present disclosure relates to a cathode, a lithium air batteryincluding the cathode, and a method of preparing the lithium airbattery.

2. Description of the Related Art

A lithium air battery employs lithium as an anode active material andair as a cathode active material, and does not need to store air in thebattery, thus enabling the battery to have a large capacity.

The theoretical specific energy of a lithium air battery may be about3,500 Watt-hours per kilogram (Wh/kg) or greater. Such a specific energyof the lithium air battery is about 10 times greater than thetheoretical specific energy of a lithium ion battery.

A cathode of a lithium air battery may be prepared by mixing acarbonaceous conductive agent, a binder, and the like. Uponcharge/discharge of a lithium air battery, a radical may be generatedduring an electrochemical reaction, and consequently, a carbonaceousconductive agent, a binder, and the like may be easily decomposed.Therefore, a lithium air battery including such a cathode may easilydeteriorate.

In addition, when a regular metal is used in a cathode of a lithium airbattery, the discharge capacity may not be sufficient.

Therefore, there is a need for a cathode for a lithium air battery thatis chemically stable against radicals generated during anelectrochemical reaction, and having excellent capacity characteristics.

SUMMARY

Provided is a cathode having excellent electronic and ionic conductivityand excellent capacity characteristics.

Provided is a lithium air battery including the cathode.

Provided is a method of preparing a lithium air battery.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of an embodiment, disclosed is a cathodeconfigured to use oxygen as a cathode active material, the cathodeincluding: a lithium alloy represented by Formula 1Li_(x)M_(y)  Formula 1wherein, in Formula 1, M is Pb, Sn, Mo, Hf, U, Nb, Th, Ta, Bi, Mg, Al,Si, Zn, Ag, Cd, In, Sb, Pt, or Au, 0<x≤10, 0<y≤10, and 0<x/y<10.

According to an aspect, a lithium air battery includes the cathode; ananode including lithium; and an electrolyte between the cathode and theanode.

According to an aspect, a method of preparing a lithium air batteryinclude: disposing an electrolyte film on an anode including lithium;disposing a metal alloyable with lithium on the electrolyte film; andelectrochemically forming a lithium alloy from the metal alloyable withlithium to form a cathode on the electrolyte film to prepare the lithiumair battery, wherein the cathode is the cathode as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a graph of voltage (Volts, V) versus lithium (x) to platinum(y) ratio in a lithium metal alloy (x/y), illustrating the potentialvaried according to the change of the lithium to platinum mole fraction(x/y);

FIG. 2 is a graph of intensity (arbitrary unit, a.u.) versus bindingenergy (electron volts, eV), illustrating a work function measured byX-ray photoelectron spectroscopy (XPS) of a lithium air batteryaccording to Example 2;

FIG. 3 is a graph of voltage (V) versus capacity (microampere-hours persquare centimeter, μAh/cm²), illustrating discharge capacity relative toa weight of a cathode for the lithium air batteries according toExamples 1 to 3 and Comparative Example 1;

FIG. 4A is a schematic view of an embodiment of an electrode structureincluding a cathode, an anode, and a solid electrolyte and a dischargeproduct formed on a surface of the cathode,

FIG. 4B is an expanded view of a portion of the electrode structure ofFIG. 4A;

FIGS. 4C to 4F are scanning electron microscope (SEM) imagescorresponding to portions of region labelled “b” in the electrodestructure shown in FIG. 4A;

FIGS. 4G and 4H are scanning electron microscope (SEM) imagescorresponding to portions of the regions labelled “c” and “d” in theelectrode structure shown in FIG. 4A;

FIGS. 5A to 5C are each a graph of intensity (a.u.) versus bindingenergy (eV), illustrating the results of XPS of the discharge productsformed on a surface of a cathode in the lithium air battery according toExample 2;

FIGS. 5D and 5E are each a graph of an atomic amount (percent, %) versussputtering time (minutes, mins), illustrating a composition ratio of thedischarge products over time;

FIG. 6 is a graph of voltage (versus lithium, V vs Li/Li⁺) versuscapacity (μAh) and Li₂O₂ thickness (nanometers, nm), showing acharge/discharge profile of the lithium air battery according to Example1 and corresponding effect on Li₂O₂ thickness;

FIG. 7 is a charge/discharge profile of the lithium air batteryaccording to Example 1 at current densities of 0.4, 2, 4, 8, 16, and 32microamperes per square centimeter (μA/cm²);

FIG. 8 is a graph of voltage (V) versus capacity (milliampere hours,mAh), showing the charge/discharge profile of the lithium air batteryaccording to Example 1 during 200 cycles; and

FIG. 9 is a schematic view illustrating an embodiment of a structure ofa lithium air battery.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In this regard, theembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Like referencenumerals refer to like elements throughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terms used in the present specification are merely used to describeparticular embodiment and are not intended to be limiting. As usedherein, “a,” “an,” “the,” and “at least one” are do not denote alimitation of quantity, and are intended to cover both the singular andplural, unless the context clearly indicates otherwise. For example, “anelement” has the same meaning as “at least one element,” unless thecontext clearly indicates otherwise. “Or” means “and/or.” As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. In the present specification, it isto be understood that the terms such as “comprises” and/or “comprising”,are intended to indicate the existence of the features, numbers, steps,actions, components, parts, ingredients, materials, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, components, parts, ingredients, materials, or combinationsthereof may exist or may be added. As used herein, “/” may be construed,depending on the context, as referring to “and” or “or”.

In the drawings, the thicknesses of layers and regions are exaggeratedor reduced for clarity. Spatially relative terms, such as “beneath,”“below,” “lower,” “above,” “upper” and the like, may be used herein forease of description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. It willbe understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is turned over, elements described as “below” or“beneath” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary term “below” canencompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

Hereinafter, a cathode and a lithium air battery including the cathodeaccording to example embodiments will be described in further detail.

A cathode according to an aspect may be configured to use oxygen as acathode active material and include a lithium alloy.

The lithium alloy included in the cathode may be structurally andchemically stable. The cathode including the lithium alloy, comparedwith a cathode including a carbonaceous conductive agent, may beprevented from decomposing when exposed to radicals and the likegenerated during electrochemical reactions. Thus, a lithium air batteryincluding the cathode may have improved charge/dischargecharacteristics. The lithium alloy is an alloy of lithium and at leastone metal other than lithium.

The lithium alloy may be an electronic conductor and a lithium ionconductor. While not wanting to be bound by theory, it is understoodthat the lithium alloy has a crystalline structure due to the inclusionof lithium, and thus the lithium alloy may provide a migration pathwayfor lithium ions. Also, the lithium alloy including lithium and at leastone metal other than lithium, may have excellent electronic conductivityand ionic conductivity. Accordingly, the lithium alloy may be a lithiumion conductor as well as an electronic conductor. Further, since thelithium alloy may serve as a lithium ion conductor, a separateelectrolyte may be omitted if desired. In an aspect, the cathode doesnot include a separate electrolyte.

According to an embodiment, the lithium alloy may be represented byFormula 1:Li_(x)M_(y)  Formula 1

wherein, in Formula 1, M may be a metal alloyable with lithium, and0<x≤10, 0<y≤10, and 0<x/y<10.

In Formula 1, M may be any metal or semimetal alloyable with lithium andis not particularly limited. For example, M may be at least one metalelement belonging to Groups 2 to 16 of the Periodic Table of Elements.

In an embodiment, in Formula 1, M may be at least one of Pb, Sn, Mo, Hf,U, Nb, Th, Ta, Bi, Mg, Al, Si, Zn, Ag, Cd, In, Sb, Pt, or Au. In anembodiment, in Formula 1, M may be at least one of Pt, Au, Ag, Sn, Zn,Mg, Al, Si, Sb, or Bi. In an embodiment, in Formula 1, M may be at leastone of Pt, Au, or Ag.

In Formula 1, x and y may indicate a molar content of Li and M inFormula 1, respectively. When where x is greater than 10, the lithiumalloy may have a low thermodynamic potential, which can be problematic.When y is greater than 10, a content of lithium may be low relative to acrystalline structure of the alloy as a whole, thus resulting in a lowionic conductivity.

For example, in Formula 1, 0<x≤10 or 0<x≤5 or 0<x≤2 or 0.05<x≤10 or0.05<x≤5 or 0.05<x≤2 or 0.1<x≤10 or 0.1<x≤5 or 0.3<x≤10 or 0.3<x≤5 or1≤x≤5 or 1≤x≤2; and in Formula 1, 0<y≤10 or 0<y≤8 or 1≤y≤10 or 1≤y≤8.

In an embodiment, in Formula 1, 0<x/y<9. In an embodiment, in Formula 1,0<x/y<5. In an embodiment, in Formula 1, 0<x/y≤2. In an embodiment, inFormula 1, 0<x/y≤1. In an embodiment, in Formula 1, 0<x/y<0.5. In anembodiment, in Formula 1, 0<x/y<0.2.

FIG. 1 is a graph of voltage (Volts, V) versus a mole fraction oflithium (x) to platinum (y) (x/y), illustrating the potential variedaccording to the change of the lithium to platinum mole fraction (x/y).As shown in FIG. 1, the potential varied according to the change of thelithium to platinum mole fraction (x/y), which is a mole fraction oflithium to M. In detail, when x is greater than y, the potential wasfound to be deteriorated. In particular, when the lithium to platinummole fraction (x/y) is greater than 2, the potential may converge toward0.

The lithium alloy may be at least one of Li_(0.06)Pt, Li_(0.14)Pt,Li_(0.33)Pt, LiPt, Li₂Pt, LiPt₇, Li_(0.06)Au, Li_(0.14)Au, Li_(0.33)Au,LiAu, Li₂Au, LiAu₇, Li_(0.06)Ag, Li_(0.14)Ag, Li_(0.33)Ag, LiAg, Li₂Ag,or LiAg₇, but the disclosed embodiment is not limited thereto.

In an embodiment, an electronic conductivity of the lithium alloy may be1.0×10⁻³ Siemens per centimeter (S/cm) or greater.

An electronic conductivity of the lithium alloy may be, for example,2.0×10⁻³ S/cm or greater, 4.0×10⁻³ S/cm or greater, 5.0×10⁻³ S/cm orgreater, 1.0×10⁻² S/cm or greater, 2.0×10⁻² S/cm or greater, 4.0×10⁻²S/cm or greater, 5.0×10⁻² S/cm or greater, 1.0×10⁻¹ S/cm or greater, or2.0×10⁻¹ S/cm or greater. Due to such a high electronic conductivity ofthe lithium alloy, internal resistance of the cathode and the lithiumair battery including the lithium alloy may decrease.

An electronic conductivity of the lithium alloy may be, for example, ina range of about 1.0×10⁻³ S/cm to about 1.0×10⁸ S/cm, about 2.0×10⁻³S/cm to about 1.0×10⁸ S/cm, about 2.0×10⁻³ S/cm to about 5.0×10⁷ S/cm,about 4.0×10⁻³ S/cm to about 5.0×10⁷ S/cm, about 4.0×10⁻³ S/cm to about1.0×10⁷ S/cm, about 5.0×10⁻³ S/cm to about 1.0×10⁷ S/cm, about 1.0×10⁻²S/cm to about 1.0×10⁷ S/cm, about 2.0×10⁻² S/cm to about 1.0×10⁷ S/cm,about 4.0×10⁻² S/cm to about 1.0×10⁷ S/cm, about 5.0×10⁻² S/cm to about1.0×10⁷ S/cm, about 1.0×10⁻¹ S/cm to about 1.0×10⁷ S/cm, about 2.0×10⁻¹S/cm to about 1.0×10⁷ S/cm, about 2.0×10⁻¹ S/cm to about 5.0×10⁶ S/cm,or about 2.0×10⁻¹ S/cm to about 1.0×10⁶ S/cm.

An ionic conductivity of the lithium alloy may be, for example, about2×10⁻³ S/cm or greater, about 4×10⁻³ S/cm or greater, about 5×10⁻³ S/cmor greater, about 1×10⁻² S/cm or greater, about 2×10⁻² S/cm or greater,about 4×10⁻² S/cm or greater, about 5×10⁻² S/cm or greater, about 1×10⁻¹S/cm or greater, or about 2×10⁻¹ S/cm or greater. Due to such a highionic conductivity of the lithium alloy, internal resistance of thecathode and the lithium battery including the lithium alloy may furtherdecrease.

An ionic conductivity of the lithium alloy may be, for example, in arange of about 1.0×10⁻³ S/cm to about 1.0×10⁻⁸ S/cm, about 2.0×10⁻³ S/cmto about 1.0×10⁻⁸ S/cm, about 2.0×10⁻³ S/cm to about 5.0×10⁻⁷ S/cm,about 4.0×10⁻³ S/cm to about 5.0×10⁻⁷ S/cm, about 4.0×10⁻³ S/cm to about1.0×10⁻⁷ S/cm, about 5.0×10⁻³ S/cm to about 1.0×10⁻⁷ S/cm, about1.0×10⁻² S/cm to about 1.0×10⁻⁷ S/cm, about 2.0×10⁻² S/cm to about1.0×10⁻⁷ S/cm, about 4.0×10⁻² S/cm to about 1.0×10⁻⁷ S/cm, about5.0×10⁻² S/cm to about 1.0×10⁻⁷ S/cm, about 1.0×10⁻¹ S/cm to about1.0×10⁻⁷ S/cm, about 2.0×10⁻¹ S/cm to about 1.0×10⁻⁷ S/cm, about2.0×10⁻¹ S/cm to about 5.0×10⁻⁶ S/cm, or about 2.0×10⁻¹ S/cm to about1.0×10⁻⁶ S/cm.

The lithium alloy may be, for example, a mixed conductor having bothlithium ionic conductivity and electron conductivity. The mixedconductor may have, for example, an electronic conductivity of 1.0×10⁻³S/cm or greater and an ionic conductivity of 1.0×10⁻³ S/cm or greater.The mixed conductor may have, for example, an electronic conductivity of1.0×10⁻³ S/cm or greater and an ionic conductivity of 2.0×10⁻³ S/cm orgreater. As the lithium alloy may serve as a mixed conductor, therebyhaving both ionic conductivity and electronic conductivity, the cathodemay omit use of an additional or a separate conductive agent and aseparate electrolyte. In an embodiment, the cathode does not include anadditional conductive agent or an additional electrolyte.

A discharge capacity of the lithium alloy may be about 1microampere-hours per square centimeter (μAh/cm²) or greater.

A discharge capacity of the lithium alloy may be, for example, 5.0μAh/cm² or greater, 1.0×10¹ μAh/cm² or greater, 2.0×10¹ μAh/cm² orgreater, 4.0×10¹ μAh/cm² or greater, 5.0×10¹ μAh/cm² or greater, 7.0×10¹μAh/cm² or greater, or 9.0×10¹ μAh/cm² or greater. Due to such a highdischarge capacity of the lithium alloy, capacity characteristics of thecathode and the lithium battery including the lithium alloy may furtherimprove.

A discharge capacity of the lithium alloy may be, for example, in arange of about 5 μAh/cm² to about 5×10³ μAh/cm², about 1×10¹ μAh/cm² toabout 5×10³ μAh/cm², about 2×10¹ μAh/cm² to about 5×10³ μAh/cm², about2×10¹ μAh/cm² to about 4×10³ μAh/cm², about 4×10¹ μAh/cm² to about 4×10³μAh/cm², about 5×10¹ μAh/cm² to about 4×10³ μAh/cm², about 7×10¹ μAh/cm²to about 3×10³ μAh/cm², or about 9×10¹ μAh/cm² to about 2×10³ μAh/cm².

In an embodiment, a discharge capacity of the lithium alloy relative toa weight of the cathode may be 100 milliampere-hours per gram of thecathode (mAh/g__(cathode)) or greater. Here, g__(cathode) refers to aweight (gram) of a cathode, and mAh/g__(cathode) refers to a unit of adischarge capacity per gram of the cathode.

A discharge capacity of the lithium alloy relative to a weight of thecathode may be, for example, 150 mAh/g__(cathode) or greater, 200mAh/g__(cathode) or greater, 250 mAh/g__(cathode) or greater, 300mAh/g__(cathode) or greater, 350 mAh/g__(cathode) or greater, 400mAh/g__(cathode) or greater, or 450 mAh/g__(cathode) or greater. When adischarge capacity of the lithium alloy relative to a weight of thecathode is within any of these ranges, capacity characteristics of thecathode and the lithium battery including the lithium alloy may furtherimprove.

A discharge capacity of the lithium alloy relative to a weight of thecathode may be, for example, in a range of about 150 mAh/g__(cathode) toabout 200,000 mAh/g__(cathode), about 200 mAh/g__(cathode) to about200,000 mAh/g__(cathode), about 200 mAh/g__(cathode) to about 150,000mAh/g__(cathode), about 250 mAh/g__(cathode) to about 150,000mAh/g__(cathode), about 300 mAh/g__(cathode) to about 150,000mAh/g__(cathode), about 350 mAh/g__(cathode) to about 150,000mAh/g__(cathode), about 400 mAh/g__(cathode) to about 150,000mAh/g__(cathode), or about 450 mAh/g__(cathode) to about 100,000mAh/g__(cathode).

The lithium alloy may be a lithium ionic conductor and may be, forexample, electrochemically stable at a voltage of 2.5 V or higher versuslithium metal.

The lithium alloy may be electrochemically stable, for example, at avoltage in a range of about 2.5 V to about 4.2 V versus lithium metal.In an aspect, the lithium alloy is not oxidized or reduced when incontact with lithium metal at a potential of about 2.5 V to about 4.2 Vversus lithium metal.

The cathode may be, for example, porous. As the cathode is porous,diffusion of air or oxygen into the cathode may be facilitated.

The cathode may further include, for example, a metal alloyable withlithium which is a precursor of the lithium alloy. In an embodiment, thecathode may include the lithium alloy represented by Formula 1 and mayfurther include a metal represented by M, wherein M is the same asdefined in Formula 1.

According to another example embodiment, a lithium metal battery mayinclude the cathode described above; an anode including lithium; and anelectrolyte between the cathode and the anode.

As the lithium air battery includes the cathode including the lithiumalloy, the lithium air battery may have improved structural stability,capacity characteristics, and lifespan characteristics.

Upon discharge of the lithium air battery, a discharge product may beformed on a surface of the cathode. That is, the discharge product maybe formed on an interface between the cathode and oxygen, rather than athree-phase interface between the cathode, a solid electrolyte, andoxygen. The formation of the discharge product may result from thesmooth migration of ions and electrons due to the cathode including thelithium alloy. Accordingly, in an embodiment, after discharge of thelithium air battery, the lithium air battery further comprises adischarge product disposed on a surface of the cathode.

For example, upon discharge of the lithium air battery, a dischargeproduct formed on a surface of the cathode may include at least one oflithium peroxide, lithium oxide, lithium hydroxide, or lithiumcarbonate. Without being limited by theory, it is understood that thedischarge product may be formed due to the electrochemical reactionbetween lithium ions transferred from a solid electrolyte membrane andoxygen used as a cathode active material.

In an embodiment, the discharge product may be at least one of Li₂O₂,LiOH, Li₂CO₃, or Li₂O, and may be Li₂O₂, LiOH, Li₂CO₃, or Li₂O, but thedischarge product is not limited thereto.

A thickness of the discharge product may be, for example, 10 micrometers(μm) or less, or about 8 μm or less, or about 5 μm or less. When athickness of the discharge product is greater than 10 μm, an energydensity of the battery may decrease.

In an embodiment, a thickness of the discharge product may be in a rangeof about 1 nm to about 10 μm, or about 1 μm to about 8 μm, or about 1 μmto about 5 μm.

The lithium air battery may include a cathode. The cathode may be an airelectrode. For example, the cathode may be disposed on a cathode currentcollector.

The cathode may include the lithium alloy described above. A content ofthe lithium alloy may be in a range of, for example, about 1 part byweight to about 100 parts by weight, about 10 parts by weight to about100 parts by weight, about 50 parts by weight to about 100 parts byweight, about 60 parts by weight to about 100 parts by weight, about 70parts by weight to about 100 parts by weight, about 80 parts by weightto about 100 parts by weight, or about 90 parts by weight to about 100parts by weight, based on 100 parts by weight of the cathode. Thecathode obtained by sintering and/or pressing lithium alloy powder maybe substantially constituted of a lithium alloy. For example, thecathode may consist essentially of, or consist of the lithium alloy.

Upon manufacture of a cathode, a pore-forming agent may be added tothereby introduce pores in the cathode. The cathode may be, for example,porous. The cathode may be, for example, in a form of a porous pellet ora porous sheet, but the disclosed embodiment is not limited thereto. Thecathode may have a porosity of about 5% to about 80%, or about 10% toabout 75%, or about 20% to about 60%. As used herein the term “porosity”is used to refer to a measure of the empty space (e.g., voids or pores)in a material and is determined as a percentage of the volume of voidsin a material based on the total volume of the material.

The size and shape of the cathode may be varied depending on the batteryshape. As the cathode consists essentially of or consists of a lithiumalloy, a structure and the manufacture of the cathode may be simplified.The cathode may be, for example, permeable to a gas such as oxygen orair. Accordingly, the cathode may be distinct from cathodes in therelated art that are substantially non-permeable to gas such as oxygenor air and conduct ions only. As the cathode is porous and/orgas-permeable, oxygen or air may be easily diffused into the cathode,and lithium ions and/or electrons may easily migrate through the lithiumalloy included in the cathode. Thus, electrochemical reactions betweenoxygen atoms, lithium ions and electrons may easily occur in thecathode.

In an embodiment, the cathode may further include, for example, acathode material other than a lithium alloy.

The cathode may include, for example, a conductive material. Such aconductive material may be, for example, porous. As the conductivematerial is porous, permeation of air into the conductive material maybe facilitated. The conductive material may be a material that is porousand/or electrically conductive. Any conductive material suitable for acathode of a lithium air battery may be used. For example, theconductive material may be a porous carbonaceous material. Examples ofthe porous carbonaceous material may include at least one of carbonblack, graphite, graphene, activated carbon, or carbon fiber. Anysuitable carbonaceous material may be used. The conductive material maybe, for example, a metallic material. The metallic material may be, forexample, at least one of a metal fiber, a metal mesh, or a metal powder.The metal powder may be, for example, at least one of copper, silver,nickel, or aluminum. The conductive material may be, for example, anelectrically conductive organic material. Examples of the electricallyconductive organic material include a polyphenylene derivative or apolythiophene derivative. A combination comprising at least two of theforegoing conductive materials may also be used. The cathode may includethe lithium alloy as the conductive material. The cathode may furtherinclude any of the above-listed conductive materials, in addition to thelithium alloy.

The cathode may further include, for example, a catalyst foroxidation/reduction of oxygen. The catalyst may be, for example, aprecious metal-based catalyst such as platinum, gold, silver, palladium,ruthenium, rhodium, and osmium; an oxide-based catalyst such asmanganese oxide, iron oxide, cobalt oxide, and nickel oxide; and anorganometallic catalyst such as cobalt phthalocyanine. However, thedisclosed embodiment is not limited thereto. Any suitable catalyst foroxidation/reduction of oxygen may be used.

For example, the catalyst may be supported on a catalyst support. Thecatalyst support may be, for example, an oxide catalyst support, azeolite catalyst support, a clay-based mineral catalyst support, or acarbon catalyst support. The oxide catalyst support may be, for example,a metal or semimetal oxide catalyst support including at least one ofAl, Si, Zr, Ti, Ce, Pr, Sm, Eu, Tb, Tm, Yb, Sb, Bi, V, Cr, Mn, Fe, Co,Ni, Cu, Nb, Mo, or W. The oxide catalyst support may include, forexample, at least one of alumina, silica, zirconium oxide, or titaniumdioxide. The carbon catalyst support may be carbon black such as Ketjenblack, acetylene black, channel black, and lamp black; a graphite suchas natural graphite, artificial graphite, and expandable graphite;activated carbon; and carbon fiber. However, the disclosed embodiment isnot limited thereto. Any suitable catalyst support available in the artmay be used. A combination comprising at least two of the foregoingcatalyst supports may also be used.

For example, the cathode may further include a binder. The binder mayinclude, for example, a thermoplastic resin or a thermocurable resin.Non-limiting examples of the binder include at least one ofpolyethylene, polypropylene, polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), styrene-butadiene rubber, atetrafluoroethylene-perfluoro (C1-C20)alkyl vinyl ether copolymer,vinylidene fluoride-hexafluoropropylene copolymer, vinylidenefluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylenecopolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer,ethylene-chlorotrifluoroethylene copolymer, vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidenefluoride-perfluoromethyl vinyl ether-tetrafluoro ethylene copolymer, orethylene-acrylic acid copolymer. Any suitable binder for a cathode maybe used.

For example, the cathode may be manufactured by mixing a conductivematerial, a catalyst for oxidation/reduction of oxygen, and a bindertogether, adding a solvent to the resulting mixture to prepare a cathodeslurry, coating the cathode slurry on a surface of a base, drying thecoated cathode slurry, and press-molding the cathode slurry against thebase to improve a density of the cathode. The base may be, for example,a cathode current collector, a separator, or a solid electrolyte film.The cathode current collector may be, for example, a gas diffusionlayer. The conductive material may include the lithium alloy. Thecatalyst for oxidation/reduction of oxygen and the binder may be omitteddepending on a type of the cathode.

The lithium air battery may include an anode. The anode may includelithium.

The anode may be, for example, a lithium metal thin film or a lithiummetal alloy-based thin film. For example, the lithium metal alloy of theanode may be an alloy of lithium with, for example, at least one ofaluminum, tin, magnesium, indium, calcium, titanium, or vanadium.

The lithium air battery may include an electrolyte between the cathodeand the anode.

The electrolyte may include at least one of a liquid electrolyte, a gelelectrolyte, or a solid electrolyte. The liquid electrolyte, the gelelectrolyte, and the solid electrolyte are not particularly limited, andmay be any suitable electrolyte for a lithium air battery.

In an embodiment, the electrolyte may include a solid electrolyte.

The solid electrolyte may include at least one of a solid electrolyteincluding an ion-conductive inorganic material, a solid electrolyteincluding a polymeric ionic liquid (PIL) and a lithium salt, a solidelectrolyte including an ion-conductive polymer and a lithium salt, asolid electrolyte including an electron-conductive polymer. However, thedisclosed embodiment is not limited thereto. Any suitable materialavailable as a solid electrolyte may be used.

The ion-conductive inorganic material may include at least one of aglass or amorphous metal ionic conductor, a ceramic active metal ionicconductor, or a glass-ceramic active metal ionic conductor. However, thedisclosed embodiment is not limited thereto. Any suitable ion-conductiveinorganic material available in the art may be used. The ion-conductiveinorganic material may be, for example, a molded product ofion-conductive inorganic particles or sheet.

For example, the ion-conductive inorganic material may be at least oneof BaTiO₃, Pb(Zr_(a)Ti_(1-a))O₃ wherein 0≤a≤1 (PZT),Pb_(1-x′)La_(x′)Zr_(1-y′)Ti_(y′)O₃ (PLZT) (where 0≤x′<1 and 0≤y′<1),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O,MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, SiC, lithiumphosphate (Li₃PO₄), lithium titanium phosphate (Li_(x)Ti_(y′), (PO₄)₃,where 0<x′<2 and 0<y′<3), lithium aluminum titanium phosphate(Li_(x′)Al_(y′)Ti_(z′)(PO₄)₃, where 0<x′<2, 0<y′<1, and 0<z′<3),Li_(1+x′+y′)(Al_(a)Ga_(1-a))_(x′)(Ti_(b)Ge_(1-b))_(2-x′)Si_(y′)P_(3-y′)O₁₂(where 0≤x′≤1, 0≤a≤1, and 0≤b≤1), lithium lanthanum titanate(Li_(x′)La_(y′)TiO₃, where 0<x′<2 and 0<y′<3), lithium germaniumthiophosphate (Li_(x′)Ge_(y′), P_(z′), S_(w′), where 0<x′<4, 0<y′<1,0<z′<1, and 0<w′<5), lithium nitride (Li_(x′)N_(y′), where 0<x′<4 and0<y<2), a SiS₂ glass (Li_(x′), Si_(y′), S_(z′), where 0<x′<3, 0<y′<2,and 0<z′<4), a P₂S₅ glass (Li_(x′)P_(y′)S_(z′), where 0<x′<3, 0<y′<3,and 0<z′<7), Li₂O, LiF, LiOH, Li₂CO₃, LiAlO₂,Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂-based ceramic, or a garnet-based ceramic(Li_(3+x′)La₃M₂O₁₂ (M=Te, Nb, or Zr), where 0≤x′≤1).

In an embodiment, the solid electrolyte may be a lithium ion-conductiveglass, a crystalline or polycrystalline lithium ion-conductive ceramic,or a crystalline or polycrystalline lithium ion-conductiveglass-ceramic. In consideration of chemical stability, the solidelectrolyte may include an oxide. In a case where the solid electrolyteincludes relatively large amounts of a lithium ion-conductive crystal, alithium alloy may have a high ionic conductivity. For example, a contentof the lithium ion-conductive crystal may be about 50 percent by weight(wt %) or greater, about 55 wt % or greater, or about 60 wt % orgreater, based on a total weight of the solid electrolyte. The lithiumion-conductive crystal may be, for example, Li₃N; a lithium superionicconductor (LISICON); a crystal having a perovskite structure, and whichis lithium ion-conductive, such as La_(0.55)Li_(0.35)TiO₃; LiTi₂P₃O₁₂having a Na superionic conductor (NASICON)-type structure; or aglass-ceramic that may precipitate these crystals. The lithium ionconductive crystal may beLi_(1+x+y)(Al_(a)Ga_(1-a))_(x)(Ti_(b)Ge_(1-b))_(2-x)Si_(y)P_(3-y)O₁₂(where 0≤x≤1, 0≤y≤1, 0≤a≤1, and 0≤b≤1, for example, 0≤x≤0.4 and 0<y≤0.6,or 0.1≤x≤0.3 and 0.1<y≤0.4). For the lithium ion-conductive crystal tohave a high ionic conductivity, the lithium ion-conductive crystal maynot have a grain boundary that hinders ion conduction. For example, aglass-ceramic may not have a pore or a grain boundary that hinders ionconduction. Thus, a glass-ceramic may have a high ion conductivity andexcellent chemical stability. Examples of a lithium ion conductiveglass-ceramic include at least one oflithium-aluminum-germanium-phosphate (LAGP),lithium-aluminum-titanium-phosphate (LATP), orlithium-aluminum-titanium-silicon-phosphate (LATSP). For example, when astarting material glass has a composition of Li₂O—Al₂O₃—TiO₂—SiO₂—P₂O₅and is heat-treated to facilitate crystallization, the major crystallinephase may be Li_(1+x+y)Al_(x)Ti_(2-x)Si_(y)P_(3-y)O₁₂ (where 0≤x≤2 and0≤y≤3). In an embodiment, x and y may be, for example, 0≤x≤0.4 and0<y≤0.6, or 0.1≤x≤0.3 and 0.1<y≤0.4. A pore or a grain boundary thathinders ion conduction refers to a material having a pore or a grainboundary that lowers the total conductivity of an inorganic materialincluding a lithium ion-conductive crystal to one tenth of aconductivity of an inorganic material including the lithiumion-conductive crystal but without a pore or a grain boundary.

In an embodiment, the solid electrolyte may include at least one oflithium-aluminum-germanium-phosphate (LAGP),lithium-aluminum-titanium-phosphate (LATP), orlithium-aluminum-titanium-silicon-phosphate (LATSP).

The polymeric ionic liquid (PIL) may include, for example, a repeatingunit including at least one cation and at least one anion. The at leastone cation may be one of an ammonium-based cation, a pyrrolidinium-basedcation, a pyridinium-based cation, pyrimidinium-based cation, animidazolium-based cation, a piperidinium-based cation, apyrazolium-based cation, an oxazolium-based cation, a pyridazinium-basedcation, a phosphonium-based cation, a sulfonium-based cation, or atriazolium-based cation. The at least one anion may be at least one ofBF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂⁻, (CF₃SO₂)₂N⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻,(C₂F₅SO₂)(CF₃SO₂)N⁻, NO₃ ⁻, Al₂Cl₇ ⁻, CH₃COO⁻, (CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻,(CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻, SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, or (O(CF₃)₂C₂(CF₃)₂O)₂PO⁻.For example, the PIL may be at least one of poly(diallyldimethylammonium) (TFSI), poly(l-allyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)imide), or poly((N-methyl-N-propylpiperidiniumbis(trifluoromethane sulfonyl)imide)).

The ion-conductive polymer may include, for example, an ion conductiverepeating unit which is derived from at least one of an ether-basedmonomer, an acryl-based monomer, a methacryl-based monomer, or asiloxane-based monomer.

The ion-conductive polymer may include, for example, at least one ofpolyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinyl pyrrolidone(PVP), polysulfone, polypropylene oxide (PPO), polymethyl methacrylate,polyethyl methacrylate, polydimethyl siloxane, polyacrylic acid,polymethacrylic acid, polymethyl acrylate, polyethyl acrylate,poly(2-ethylhexyl acrylate), polybutyl methacrylate, poly (2-ethylhexylmethacrylate), polydecyl acrylate, polyethylene vinylacetate, aphosphate ester polymer, polyester sulfide, polyvinylidene fluoride(PVdF), or Li-substituted Nafion. However, the disclosed embodiment isnot limited thereto. Any suitable material for an ion-conductive polymermay be used.

The electron-conductive polymer may be, for example, at least one of apolyphenylene derivative, or a polythiophene derivative. However, thedisclosed embodiment is not limited thereto. Any suitableelectron-conductive polymer available in the art may be used.

For example, the gel electrolyte may be obtained by adding alow-molecular weight solvent to the solid electrolyte between thecathode and the anode. For example, the gel electrolyte may be obtainedby adding a solvent, which is a low-molecular weight organic compound,or an oligomer into a polymer. For example, the gel electrolyte may beobtained by adding a solvent, which is a low-molecular weight organiccompound, or an oligomer into the polymer electrolyte described above.

For example, the liquid electrolyte may include a solvent and a lithiumsalt.

The solvent may include at least one selected from an organic solvent,an ionic liquid, and an oligomer. However, the disclosed embodiment isnot limited thereto. Any suitable solvent that is in liquid form at roomtemperature (25° C.) available in the art may be used.

The organic solvent may include, for example, at least one of anether-based solvent, a carbonate-based solvent, an ester-based solvent,or a ketone-based solvent. For example, the organic solvent may includeat least one of propylene carbonate, ethylene carbonate, fluoroethylenecarbonate, vinylethylene carbonate, butylene carbonate, dimethylcarbonate, diethyl carbonate, methylethyl carbonate, methylpropylcarbonate, ethylpropyl carbonate, methylisopropyl carbonate, dipropylcarbonate, dibutyl carbonate, benzonitrile, acetonitrile,tetrahydrofuran, 2-methyl tetrahydrofuran, γ-butyrolactone, dioxorane,4-methyldioxorane, dimethyl acetamide, dimethylsulfoxide, dioxane,1,2-dimethoxyethane, sulforane, dichloroethane, chlorobenzene,nitrobenzene, succinonitrile, diethylene glycol dimethyl ether (DEGDME),tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycoldimethyl ether (PEGDME, Mn=about 500), dimethyl ether, diethyl ether,dibutyl ether, or dimethoxyethane. However, the disclosed embodiment isnot limited thereto. Any suitable organic solvent in liquid form at roomtemperature may be used.

The ionic liquid (IL) may include, for example, a cation and an anion.The cation may be at least one of an ammonium-based cation, apyrrolidinium-based cation, a pyridinium-based cation,pyrimidinium-based cation, an imidazolium-based cation, apiperidinium-based cation, a pyrazolium-based cation, an oxazolium-basedcation, a pyridazinium-based cation, a phosphonium-based cation, asulfonium-based cation, or a triazolium-based cation. The anion may beat least one of BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻,CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻, CF₃SO₃ ⁻,(C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N—, NO₃ ⁻, Al₂Cl₇ ⁻, CH₃COO⁻,(CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻,SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃ ⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, or(O(CF₃)₂C₂(CF₃)₂O)₂PO⁻.

The lithium salt may include, for example, at least one of LiTFSI(LiN(SO₂CF₃)₂), LiPF₆, LiBF₄, LiAsF₆, LiClO₄, LiNO₃, lithiumbis(oxalato) borate (LiBOB), LiN(SO₂C₂F₅)₂, LiC(SO₂CF₃)₃, LiN(SO₃CF₃)₂,LiC₄F₉SO₃, LiAlCl₄, or lithium trifluoromethanesulfonate (LiCF₃SO₃,LiTfO). However, the disclosed embodiment is not limited thereto. Anysuitable lithium salt may be used. A concentration of the lithium saltmay be, for example, in a range of about 0.01 molar (M) to about 5 M.

In an embodiment, the lithium air battery may further include, forexample, a separator between the cathode and the anode. The separatormay be any suitable separator having a composition durable under usageenvironments of a lithium air battery. For example, the separator may beat least one of a polymeric non-woven fabric such as a polypropylenenon-woven fabric or a polyphenylene sulfide non-woven fabric; a porousfilm of an olefin-based resin such as polyethylene or polypropylene; orglass fiber.

For example, the electrolyte membrane may have a structure including aseparator impregnated with a solid polymer electrolyte or a liquidelectrolyte. The electrolyte membrane including a separator impregnatedwith a solid polymer electrolyte may be prepared by disposing a solidpolymer electrolyte film on one or both surfaces of the separator whileperforming roll-pressing thereon at the same time. In an embodiment, theelectrolyte membrane including a separator impregnated with a liquidelectrolyte may be prepared by injecting the liquid electrolyteincluding a lithium salt into the separator.

According to still another aspect, a method of preparing a lithium airbattery may include:

disposing an electrolyte film on an anode including lithium;

disposing a metal alloyable with lithium on the electrolyte film; and

electrochemically forming a lithium alloy from the metal alloyable withlithium to form a cathode on the electrolyte film.

In an embodiment, the electrolyte film may be a solid electrolyte film.

In an embodiment, the cathode, the electrolyte film, and the anode mayeach be understood by referring to the descriptions for the cathode, theelectrolyte, and the anode described above.

The electrochemical formation of the lithium alloy may includeelectrochemically doping the lithium on the metal alloyable withlithium. The method of electrochemically doping the metal with thelithium may not be particularly limited. Any suitable doping method maybe used.

The lithium air battery according to an embodiment may be prepared by amethod known to those of skill in the art without undue experimentation.

For example, after the anode is mounted on an inner side of a case, theelectrolyte membrane may be disposed on the anode, the cathode may bedisposed on the electrolyte membrane, a porous cathode current collectormay be disposed on the cathode, and a pressing member that allowstransfer of air into the air electrode and which pushes the porouscathode current collector to fix the cell, may be disposed on thecathode current collector, thereby completing the manufacture of thelithium air battery. The case may be divided into upper and lower partsthat contact the anode and the air electrode, respectively. Aninsulating resin may be between the upper and lower parts toelectrically insulate the cathode and the anode from each other.

The lithium air battery may be a lithium primary battery or a lithiumsecondary battery. The lithium air battery is not limited to a specificshape, and may have, for example, a shape like a coin, a button, asheet, a stack, a cylinder, a plane, or a horn. The lithium air batterymay be used as a large battery for an electric vehicle.

FIG. 9 is a schematic view illustrating an embodiment of a structure ofa lithium air battery 500. Referring to FIG. 9, the lithium air battery500 may include a cathode 200 adjacent to a first current collector 210and using oxygen as an active material, an anode 300 adjacent to asecond current collector 310 and including lithium, and a firstelectrolyte membrane 400 between the cathode 200 and the anode 300. Thefirst electrolyte membrane 400 may be a separator impregnated with aliquid electrolyte. A second electrolyte membrane 450 may be between thecathode 200 and the first electrolyte membrane 400. The secondelectrolyte membrane 450 may be a lithium ion conductive solidelectrolyte film. The first current collector 210, which is porous, mayserve as a gas diffusion layer. Also, a pressing member 220 that allowsair to reach the cathode 200 may be on the first current collector 210.A case 320 formed of an insulating resin between the cathode 200 and theanode 300 may electrically insulate the cathode 200 and the anode 300from each other. Air may be supplied through an air inlet 230 a and bedischarged through an air outlet 230 b. The lithium air battery 500 maybe accommodated in a stainless steel (SUS) container (not shown).

The term “air” as it relates to a lithium air battery, as used herein,is not limited to atmospheric air, and may refer to any suitablecombination of gases including oxygen, or pure oxygen gas. This broaddefinition of “air” also applies to other terms including “air battery”and “air electrode”.

Hereinafter example embodiments will be described in detail withreference to Examples and Comparative Examples. These examples areprovided for illustrative purposes only and are not intended to limitthe scope of the present inventive concept.

EXAMPLES Preparation of Lithium Air Battery Example 1: Preparation ofLithium Air Battery (Cathode/LATP/PEGDME/Li Anode)

A polymeric electrolyte was disposed as an intermediate layer on alithium metal foil having a thickness of 260 μm (available from OharaCorp., Japan) serving as an anode. The polymeric electrolyte wasprepared by mixing polyethylene glycol dimethylether (PEGDME, Mn=500Daltons) with a lithium salt, i.e., lithiumbis(trifluoromethylsulfonyl)imide (LiTFSI), such that a molar ratiobetween PEGDME to Li was 20:1.

A solid electrolyte film, i.e., a lithium aluminum titanium phosphate(LATP) film having a thickness of 260 μm (available from Ohara Corp.,Japan) was disposed on the polymeric electrolyte.

A layer of platinum (Pt) metal having a thickness of 8 nanometers (nm)was formed on the solid electrolyte film, and the Pt metal was dopedwith lithium at a current density of 0.4 microamperes per squarecentimeter (μA/cm²), thereby forming a Li_(x)Pt_(y) alloy cathode. Thecharge and discharge were performed at a current density in a range of0.4 μA/cm² to 32 μA/cm².

Next, a nickel mesh was disposed on the cathode, and a pressing memberthat allows air to reach the cathode may apply pressure to fix the cell,was added, thereby completing the preparation of the lithium airbattery.

Example 2

A lithium air battery was prepared in substantially the same manner asin Example 1, except that a layer of gold (Au) metal having a thicknessof 8 nm was used instead of Pt metal having a thickness of 8 nm. Here, abinding energy of Au 4f electrons was measured by X-ray photoelectronspectroscopy (XPS) of the cathode/LATP/PEGDME/Li anode structure in theprepared lithium air battery, the results of which are shown in FIG. 2.

Further, a schematic view of the cathode/LATP/PEGDME/Li anode structureis shown in FIGS. 4A and 4B, and SEM images of each site are shown inFIGS. 4C to 4H.

FIGS. 4C to 4F are scanning electron microscope (SEM) imagescorresponding to portions of region labelled “b” in the electrodestructure shown in FIG. 4A and FIGS. 4G and 4H are scanning electronmicroscope (SEM) images corresponding to portions of the regionslabelled “c” and “d” in the electrode structure shown in FIG. 4A. Asshown in FIGS. 4A to 4H, a cathode 200 including the lithium alloy Li—Aualloy was formed, and a discharge product 600 was formed on a surface ofthe lithium alloy.

In particular, as shown in FIGS. 4C to 4H, a discharge product wasformed only on the alloy, thereby showing maximum 10 μm of growth.

Example 3

A lithium air battery was prepared in substantially the same manner asin Example 1, except that a layer of silver (Ag) metal having athickness of 8 nm was used instead of the Pt metal having a thickness of8 nm.

Comparative Example 1

A lithium air battery was prepared in substantially the same manner asin Example 1, except that a layer of nickel (Ni) metal having athickness of 8 nm was used instead of the Pt metal having a thickness of8 nm.

Comparative Example 2

A lithium air battery was prepared in substantially the same manner asin Example 1, except that a layer of copper (Cu) metal having athickness of 8 nm was used instead of the Pt metal having a thickness of8 nm.

Evaluation Example 1: Evaluation of Electronic Conductivity

Both surfaces of the cathodes used in the lithium air batteries preparedin Examples 1 to 3 and Comparative Examples 1 and 2 were subjected tosputtering with gold to thereby form an ion blocking cell. Theelectronic conductivity thereof was measured by using a 4-point probemethod.

A time-dependent current was measured, which was obtained while applyinga constant voltage of 100 millivolts (mV) to the complete symmetric cellfor 30 minutes. An electronic resistance of the cathode was calculatedfrom the measured current, and an electronic conductivity was calculatedfrom the electronic resistance. The results of measured electronicconductivity are shown in Table 1.

TABLE 1 Cathode Electronic conductivity composition [S/cm] Example 1Li_Pt_(—) 5.2 × 10⁵ Example 2 Li_Au_(—) 1.4 × 10⁵ Example 3 Li_Ag_(—)3.0 × 10³ Comparative Example 1 Ni 1.4 × 10⁵ Comparative Example 2 Cu5.6 × 10⁶

Evaluation Example 2: Evaluation of Discharge Capacity

The lithium air batteries prepared in Examples 1 to 3 and ComparativeExamples 1 and 2 were subjected to discharge to a voltage of 2.0 V (vs.Li) at a constant current of μA/cm² at a temperature of 60° C., atatmospheric pressure (1 atm), and under an oxygen atmosphere. Thedischarge capacity and the discharge capacity relative to the cathodewere each measured, of which the results are shown in Table 2 and FIG.3.

TABLE 2 Discharge Discharge capacity relative capacity to the cathode(μAh/cm²) (mAh/g_(—) _(cathode)) Example 1 1,071 89,400 Example 2 24328,200 Example 3 98 47,700 Comparative Example 1 0.1 8 ComparativeExample 2 0.1 8

Evaluation Example 3: Evaluation of Discharge Product

The discharge product formed on a surface of the cathode in the lithiumair battery prepared in Example 2 was subjected to XPS spectrum andelement composition measurement. The results thereof are shown in FIGS.5A to 5E.

As shown FIGS. 5A to 5E, the discharge product may be lithium peroxide(Li₂O₂), lithium oxide (Li₂O), lithium hydroxide (LiOH), or lithiumcarbonate (Li₂CO₃). Also, a portion of the lithium alloy cathode wasfound to be included in the discharge product.

Evaluation Example 4: Evaluation of Charge/Discharge Characteristics

The lithium air battery prepared in Example 1 was discharged at aconstant current of 0.4, 2, 4, 8, 16, or 32 μA/cm² for 1 hour attemperature of 60° C., at atmospheric pressure (1 atm), and under anoxygen atmosphere. Then, charging was performed with the same currentfor 1 hour to perform charge/discharge cycles, the results of which areshown in FIG. 7. FIG. 6 shows the charge/discharge test result in thefirst cycle.

As shown in FIGS. 6 and 7, the lithium air battery employing the cathodeincluding the lithium alloy was found to have excellent charge/dischargecharacteristics.

Evaluation Example 5: Evaluation of Cycle Characteristics

The lithium air battery prepared in Example 1 was discharged at aconstant current of 0.0013 mA/cm² for 1 hour at temperature of 60° C.,at atmospheric pressure (1 atm), and under an oxygen atmosphere. Then,charging was performed with the same current for 1 hour to performcharge/discharge cycles. Here, cut-off voltage was in a range of 2.8 Vto 4.2 V (vs. Li). This cycle was performed 400 times. The graph ofcharge/discharge is shown in FIG. 8.

Referring to FIG. 8, the lithium air battery employing the cathodeincluding the lithium alloy was found to have excellent cyclecharacteristics.

It should be understood that the disclosed embodiment described hereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould be considered as available for other similar features or aspectsin other embodiments.

While an embodiment has been described with reference to the figures, itwill be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope as defined by the following claims.

What is claimed is:
 1. A cathode configured to use oxygen as a cathode active material, the cathode comprising a lithium alloy layer.
 2. The cathode of claim 1, wherein the lithium alloy layer is an electronic conductor and a lithium ion conductor.
 3. The cathode of claim 1, wherein the lithium alloy layer is represented by Formula 1: Li_(x)M_(y)  Formula 1 wherein, in Formula 1, M is a metal alloyable with lithium, and 0<x≤10, 0<y≤10, and 0<x/y<10.
 4. The cathode of claim 3, wherein, in Formula 1, M is at least one of Pb, Sn, Mo, Hf, U, Nb, Th, Ta, Bi, Mg, Al, Si, Zn, Ag, Cd, In, Sb, Pt, or Au.
 5. The cathode of claim 3, wherein, in Formula 1, 0<x/y<5.
 6. The cathode of claim 1, wherein the lithium alloy layer is at least one of Li_(0.06)Pt, Li_(0.14)Pt, Li_(0.33)Pt, LiPt, Li₂Pt, LiPt₇, Li_(0.06)Au, Li_(0.14)Au, Li_(0.33)Au, LiAu, Li₂Au, LiAu₇, Li_(0.06)Ag, Li_(0.14)Ag, Li_(0.33)Ag, LiAg, Li₂Ag, or LiAg₇.
 7. The cathode of claim 1, wherein an electronic conductivity of the lithium alloy layer is about 1.0×10⁻³ Siemens per centimeter (S/cm) or higher.
 8. The cathode of claim 1, wherein a discharge capacity of the lithium alloy layer is about 1.0 microampere-hour per square centimeter (μAh/cm²) or greater.
 9. The cathode of claim 1, wherein a discharge capacity of the lithium alloy layer relative to a weight of the cathode is about 100 milliampere-hours per gram of the cathode (mAh/g__(cathode)) or greater.
 10. The cathode of claim 1, wherein the lithium alloy layer is electrochemically stable at a voltage of about 2.5 volts (V) or greater versus (vs.) lithium metal.
 11. The cathode of claim 1, further comprising a metal that is a precursor of the lithium alloy layer.
 12. The cathode of claim 1, wherein the cathode is porous.
 13. A lithium air battery comprising: the cathode of claim 1; an anode comprising lithium; and an electrolyte between the cathode and the anode.
 14. The lithium air battery of claim 13, wherein the lithium air battery further comprises a discharge product disposed on a surface of the cathode, wherein the discharge product comprises at least one of lithium peroxide, lithium oxide, lithium hydroxide, or lithium carbonate.
 15. The lithium air battery of claim 14, wherein a thickness of the discharge product is about 10 micrometers (μm) or less.
 16. The lithium air battery of claim 14, wherein the discharge product is at least one of Li₂O₂, LiOH, Li₂CO₃, or Li₂O.
 17. The lithium air battery of claim 13, wherein the electrolyte comprises a solid electrolyte.
 18. The lithium air battery of claim 17, wherein the solid electrolyte is at least one of a lithium ion-conductive glass, a crystalline lithium ion-conductive ceramic, or a crystalline lithium ion-conductive glass-ceramic.
 19. The lithium air battery of claim 17, wherein the solid electrolyte comprises at least one of lithium-aluminum-germanium-phosphate (LAGP), lithium-aluminum-titanium-phosphate (LATP), or lithium-aluminum-titanium-silicon-phosphate (LATSP).
 20. A method of preparing the lithium air battery of claim 13, the method comprising: disposing an electrolyte film on the anode; disposing a metal alloyable with lithium on the electrolyte film; and electrochemically forming a lithium alloy layer from the metal alloyable with lithium to form the cathode on the electrolyte film to prepare the lithium air battery.
 21. The method of claim 20, wherein the electrolyte film is a solid electrolyte film. 